Within the last few years there has been great interest in the use and application of binary or diffractive optical elements (DOE's). A DOE is created by etching microscopic patterns on the surface of a substrate. The edges of the patterns diffract light. With the proper design, the DOE can be used like a standard refractive lens to focus light.
The fabrication steps used in creating various DOEs are known in the art. See, for example, the disclosure in U.S. Pat. Nos. 4,846,552 and 4,895,790 both incorporated herein by reference. An alternative fabrication technique is disclosed in copending application Ser. No. 07/479,474 filed Feb. 13, 1990.
The steps used to construct a DOE are similar to semiconductor fabrication techniques. In fact, off-the shelf semiconductor photomask and etching equipment can be used. A computer program is used to calculate the configuration of the photomasks. The efficiency of the optic is improved as the number of masking and etching steps is increased.
Now that the theory and technology related to DOE's has been demonstrated, there is significant interest in developing a wide range of applications for the devices. It has been reported that DOE's are being incorporated into bifocal implants used for cataract patients. Another commonly cited application is the addition of a DOE surface to a standard spherical lens to correct for chromatic aberrations. As is well known, standard refractive lenses will focus different wavelengths of light at different locations. In the prior art, such chromatic errors were corrected using additional lenses. In contrast, chromatic aberrations can be corrected in a single lens by etching a properly designed DOE pattern on the surface of a refractive lens.
In the prior art there has also been discussions relating to the use of DOE's with lasers. Due to their lightweight and relatively low cost, DOE's have been suggested as replacements for lenses in compact disc players for focusing the beams from laser diodes. In addition, a DOE can be used to shape a laser beam after it has been emitted from the laser. For example, U.S. Pat. No. 4,933,649 teaches that the side lobes of a laser diode array can be suppressed by using a DOE in a corrective optical system.
Up to this time, there has been no detailed study regarding integrating DOE's into a laser resonator. Beyond the obvious appeal of lower costs, a number of added benefits can be realized if a DOE is incorporated into the design of a laser resonator.
Accordingly, it is an object of the subject invention to provide a laser utilizing a diffractive optical element.
It is a further object of the subject invention to provide a laser wherein a DOE is formed integrally with one or more end mirrors of a laser resonator.
It is another object of the subject invention to provide a laser wherein a DOE is formed integrally with the gain medium.
It is still a further object of the subject invention to provide a laser wherein a DOE is used to control the shape of the transverse mode of the circulating laser beam.
It is still another object of the subject invention to provide a laser wherein a DOE is used to control the shape of the transverse mode of the laser beam emitted from the cavity.
It is still another object of the subject invention to provide a laser with a DOE formed on a radiused optic.
It is still another object of the subject invention to provide a laser with a DOE in combination with multilayer stacks configured for applications such as antireflection or wavelength selection.